The integrase promoter of bacteriophage lambda will be localized and its properties probed through two types of genetic interruptions: insertion of tetracycline transposons, and fusions to the bacterial trp promoter. A new process by which a lambda bio phase carrying the insertion sequence IS1 appears to insert into the bacterial chromosome by means of the IS1 will be characterized by deletion mapping of the prophage in various insertion strains. Regulation of biotin biosynthesis in E. coli will be studied in strains where the beta-galactosidase gene is fused to biotin promoters. BIBLIOGRAPHIC REFERENCES: Campbell, Allan. Significance of constitutive integrase synthesis, Proc. Nat. Acad. Sci. USA 73: 3 (1976).